U.S. patent application number 13/406771 was filed with the patent office on 2013-08-29 for efficient link repair mechanism triggered by data traffic.
This patent application is currently assigned to Cisco Technology, Inc.. The applicant listed for this patent is Navneet Agarwal, Jean-Philippe Vasseur. Invention is credited to Navneet Agarwal, Jean-Philippe Vasseur.
Application Number | 20130227336 13/406771 |
Document ID | / |
Family ID | 49004627 |
Filed Date | 2013-08-29 |
United States Patent
Application |
20130227336 |
Kind Code |
A1 |
Agarwal; Navneet ; et
al. |
August 29, 2013 |
EFFICIENT LINK REPAIR MECHANISM TRIGGERED BY DATA TRAFFIC
Abstract
In one embodiment, an intermediate device transmits a data
message away from a root device toward a receiver device in a
computer network, the data message transmitted by utilizing, in
reverse, a link that had been previously selected by the receiver
device toward the root device. In response to detecting that the
data message did not reach the receiver device, a discovery message
is may be sent to one or more neighbor devices, wherein the
discovery message carries an identification (ID) of the receiver
device and a discovery scope indicating how many hops the discovery
message is allowed to traverse to reach the receiver device, and
wherein the receiver device, upon receiving the discovery message,
triggers a local link repair of the link from the receiver device
toward the root device.
Inventors: |
Agarwal; Navneet;
(Bangalore, IN) ; Vasseur; Jean-Philippe; (Saint
Martin d'Uriage, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Agarwal; Navneet
Vasseur; Jean-Philippe |
Bangalore
Saint Martin d'Uriage |
|
IN
FR |
|
|
Assignee: |
Cisco Technology, Inc.
San Jose
CA
|
Family ID: |
49004627 |
Appl. No.: |
13/406771 |
Filed: |
February 28, 2012 |
Current U.S.
Class: |
714/4.3 ;
714/E11.023 |
Current CPC
Class: |
H04L 45/22 20130101;
H04L 43/0811 20130101; H04L 45/28 20130101; H04L 45/02 20130101;
H04L 45/14 20130101; H04L 41/0677 20130101 |
Class at
Publication: |
714/4.3 ;
714/E11.023 |
International
Class: |
G06F 11/07 20060101
G06F011/07 |
Claims
1. A method, comprising: transmitting, by an intermediate device, a
data message away from a root device toward a receiver device in a
computer network, the data message transmitted by utilizing, in
reverse, a link that had been previously selected by the receiver
device toward the root device; detecting that the data message did
not reach the receiver device; and in response to detecting that
the data message did not reach the receiver device, sending a
discovery message to one or more neighbor devices, wherein the
discovery message carries an identification (ID) of the receiver
device and a discovery scope indicating how many hops the discovery
message is allowed to traverse to reach the receiver device, and
wherein the receiver device, upon receiving the discovery message,
triggers a local link repair of the link from the receiver device
toward the root device.
2. The method as in claim 1, further comprising: maintaining a
one-hop neighbor list at the intermediate device; and sending the
discovery message to the one or more neighbor devices from the
one-hop neighbor list.
3. The method as in claim 1, further comprising: sending the
discovery message to only neighbor devices that are as far as or
further than the intermediate device from the root device.
4. The method as in claim 1, wherein sending the discovery message
comprises one of either unicasting the discovery message or
multicasting the discovery message.
5. The method as in claim 1, further comprising: sending the
discovery message one discovery scope level at a time, wherein each
neighbor device receiving the discovery message checks whether it
can reach the receiver device, and if so, notifies the intermediate
device, and if not, delays a configured time before forwarding the
discovery message to a next discovery scope level; and sending, in
response to receiving a notification at the intermediate device
that a particular neighbor device can reach the receiver device, an
instruction to each other neighbor device to cease forwarding the
discovery message.
6. The method as in claim 1, further comprising: encapsulating the
data message within the discovery message.
7. The method as in claim 1, further comprising: receiving, from a
particular neighbor device that can reach the receiver device, a
reply to the discovery message, wherein the reply carries a proper
path to the receiver device.
8. The method as in claim 1, wherein the discovery message is
originated by one of either the intermediate device, or a source of
the data message after having been notified that the data message
did not reach the receiver device.
9. The method as in claim 1, further comprising: determining that
the discovery message did not result in reaching the receiver
device; and in response, increasing the discovery scope of a
subsequently sent discovery message to the receiver device.
10. A method, comprising: receiving a discovery message at a
particular device in response to an intermediate device detecting
that a data message transmitted away from a root device toward a
receiver device in a computer network did not reach the receiver
device, wherein the data message was transmitted utilizing, in
reverse, a link that had been previously selected by the receiver
device toward the root device, wherein the discovery message
carries an identification (ID) of the receiver device and a
discovery scope indicating how many hops the discovery message is
allowed to traverse to reach the receiver device; determining
whether the receiver device is reachable by the particular device;
and in response to the receiver device being reachable, forwarding
the discovery message to the receiver device, wherein the receiver
device, upon receiving the discovery message, triggers a local link
repair of the link from the receiver device toward the root device;
and is in response to the receiver device not being reachable,
decrementing the discovery scope, and, if the decremented discovery
scope is non-zero, forwarding the discovery message to one or more
neighbor devices of the particular device.
11. The method as in claim 10, further comprising: maintaining a
one-hop neighbor list at the particular device; and forwarding the
discovery message to the one or more neighbor devices from the
one-hop neighbor list.
12. The method as in claim 10, further comprising: sending the
discovery message to only neighbor devices that are as far as or
further than the particular device from the root device.
13. The method as in claim 10, wherein forwarding the discovery
message comprises one of either unicasting the discovery message or
multicasting the discovery message.
14. The method as in claim 10, further comprising: forwarding the
discovery message one discovery scope level at a time, wherein each
neighbor device receiving the discovery message checks whether it
can reach the receiver device, and if so, notifies the particular
device, and if not, delays a configured time before forwarding the
discovery message to a next discovery scope level; and sending, in
response to receiving a notification at the particular device that
a particular neighbor device can reach the receiver device, an
instruction to each other neighbor device to cease forwarding the
discovery message.
15. The method as in claim 10, further comprising: in response to
the receiver device being reachable over a proper path, returning a
reply to the discovery message, wherein the reply carries a proper
path to the receiver device.
16. A method, comprising: determining a selected link from a
particular device toward a root device in a computer network,
wherein traffic destined away from the root device via the
particular device utilizes the selected link in reverse from an
intermediate device; receiving a discovery message at the
particular device in response to the intermediate device detecting
that a data message transmitted over the selected link in reverse
did not reach the particular device, wherein the discovery message
is received from a neighbor device other than the intermediate
device; and in response to receiving the discovery message,
triggering a local link repair of the selected link from the
particular device toward the root device to determine a new
selected link from the particular device toward the root device,
wherein traffic destined away from the root device via the
particular device utilizes the new selected link in reverse from
another intermediate device.
17. The method as in claim 16, further comprising: receiving a data
message at the particular device over an improper, unselected link
from a given intermediate device; and notifying the given
intermediate device of the improper use of the unselected link.
18. The method as in claim 17, further comprising: determining that
more than a configured number of improper uses of unselected links
have occurred at the particular device; and in response, notifying
a management device of the improper uses, wherein the management
device is configured to take corrective action regarding the
improper uses.
19. The method as in claim 16, further comprising: decapsulating
the data message from within the discovery message.
20. An apparatus, comprising: one or more network interfaces to
communicate in a computer network; a processor coupled to the
network interfaces and adapted to execute one or more processes;
and a memory configured to store a process executable by the
processor, the process when executed operable to: generate and
transmit a discovery message in response to a data message sent
away from a root device of the computer network not reaching an
intended receiver device over a link that had been previously
selected, in reverse, by the receiver device toward the root
device; receive a discovery message for a first intermediate device
transmitting a different data message and to forward the discovery
messages to the receiver device if reachable, else, in response to
the receiver device not being reachable, decrement a discovery
scope of the discovery messages, and forward a discovery message
with a non-zero scope to one or more neighbor devices; and receive
a discovery message intended for the apparatus in response to a
second intermediate device detecting that a data message did not
reach the apparatus over a link previously selected, in reverse,
from the apparatus to the second intermediate device, and to
trigger a local link repair of the previously selected link in
response.
21. The apparatus as in claim 20, wherein the process when executed
is further operable to: receive a data message over an improper,
unselected link from a given intermediate device; and notify the
given intermediate device of the improper use of the unselected
link.
22. A tangible, non-transitory, computer-readable media having
software encoded thereon, the software, when executed by a
processor on an apparatus, operable to: generate and transmit a
discovery message in response to a data message sent away from a
root device of the computer network not reaching an intended
receiver device over a link that had been previously selected, in
reverse, by the receiver device toward the root device; receive a
discovery message for a first intermediate device transmitting a
different data message and to forward the discovery messages to the
receiver device if reachable, else, in response to the receiver
device not being reachable, decrement a discovery scope of the
discovery messages, and forward a discovery message with a non-zero
scope to one or more neighbor devices; and receive a discovery
message intended for the apparatus in response to a second
intermediate device detecting that a data message did not reach the
apparatus over a link previously selected, in reverse, from the
apparatus to the second intermediate device, and is to trigger a
local link repair of the previously selected link in response.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to computer
networks, and, more particularly, to mainlining links in computer
networks.
BACKGROUND
[0002] Low power and Lossy Networks (LLNs), e.g., sensor networks,
have a myriad of applications, such as Smart Grid and Smart Cities.
Various challenges are presented with LLNs, such as lossy links,
low bandwidth, battery operation, low memory and/or processing
capability, etc. One example routing solution to LLN challenges is
a protocol called Routing Protocol for LLNs or "RPL," which is a
distance vector routing protocol that builds a Destination Oriented
Directed Acyclic Graph (DODAG, or simply DAG) in addition to a set
of features to bound the control traffic, support local (and slow)
repair, etc. The RPL architecture provides a flexible method by
which each node performs DODAG discovery, construction, and
maintenance.
[0003] One significant challenge with routing in LLNs is ensuring
that links to neighboring nodes are valid. More traditional IP
networks typically use a proactive keepalive mechanism with a
relatively short period, such as the Bidirectional Forwarding
Detection (BFD) protocol. Due to the strict resource constraints of
LLNs, protocols such as RPL do not rely on proactive keepalive
mechanisms. Instead, many LLN protocols typically take a reactive
approach, using link-layer acknowledgments and/or IPv6 Neighbor
Unreachability Detection (NUD) to update link statistics when
forwarding traffic.
[0004] One fundamental problem is that nodes in many LLNs only
maintain links in the UPWARD direction (toward a root node), and
detect link failures reactively when sending a data packet. If a
node has no data packets to send, it will not detect the link
failure and will not notify the root that the link is no longer
valid. As a result, the root will continue to send traffic down an
invalid path.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The embodiments herein may be better understood by referring
to the following description in conjunction with the accompanying
drawings in which like reference numerals indicate identically or
functionally similar elements, of which:
[0006] FIG. 1 illustrates an example communication network;
[0007] FIG. 2 illustrates an example network device/node;
[0008] FIG. 3 illustrates an example message format;
[0009] FIG. 4 illustrates an example directed acyclic graph (DAG)
in the communication network as in FIG. 1;
[0010] FIG. 5 illustrates an example data message exchange;
[0011] FIGS. 6A-6C illustrate examples of discovery message
exchanges;
[0012] FIG. 7 illustrates an example discovery message format;
[0013] FIGS. 8A-8D illustrate further example discovery message
exchanges;
[0014] FIG. 9 illustrates an example local link repair;
[0015] FIGS. 10A-10C illustrate an example of serialized discovery
message exchanges;
[0016] FIGS. 11A-11B illustrate an example of improper path
utilization;
[0017] FIG. 12 illustrates an example simplified procedure for
efficient link repair mechanism triggered by data traffic in a
computer network, particularly from the perspective of the device
utilizing the broken/improper link;
[0018] FIG. 13 illustrates an example simplified procedure for
efficient link repair mechanism triggered by data traffic in a
computer network, particularly from the perspective of a neighbor
device attempting to reach the receiver device;
[0019] FIG. 14 illustrates an example simplified procedure for
efficient link repair mechanism triggered by data traffic in a
computer network, particularly from the perspective of the receiver
device; and
[0020] FIG. 15 illustrates another example simplified procedure for
efficient link repair mechanism triggered by data traffic in a
computer network, particularly from the perspective of the receiver
device when a link is used improperly.
DESCRIPTION OF EXAMPLE EMBODIMENTS
Overview
[0021] According to one or more embodiments of the disclosure, an
intermediate device transmits a data message away from a root
device toward a receiver device in a computer network, the data
message transmitted by utilizing, in reverse, a link that had been
previously selected by the receiver device toward the root device.
In response to detecting that the data message did not reach the
receiver device, a discovery message is may be sent to one or more
neighbor devices, wherein the discovery message carries an
identification (ID) of the receiver device and a discovery scope
indicating how many hops the discovery message is allowed to
traverse to reach the receiver device, and wherein the receiver
device, upon receiving the discovery message, triggers a local link
repair of the link from the receiver device toward the root
device.
[0022] According to one or more additional embodiments of the
disclosure, a discovery message may be received at a particular
device in response to an intermediate device detecting that a data
message transmitted away from a root device toward a receiver
device in a computer network did not reach the receiver device,
wherein the data message was transmitted utilizing, in reverse, a
link that had been previously selected by the receiver device
toward the root device, wherein the discovery message carries an
identification (ID) of the receiver device and a discovery scope
indicating how many hops the discovery message is allowed to
traverse to reach the receiver device. In response to the receiver
device being reachable by the particular device, the discovery
message may be forwarded to the receiver device, wherein the
receiver device, upon receiving the discovery message, triggers a
local link repair of the link from the receiver device toward the
root device. Alternatively, in response to the receiver device not
being reachable, the discovery scope is decremented, and, if the
decremented discovery scope is non-zero, the discovery message may
then be forwarded to one or more neighbor devices of the particular
device.
[0023] According to one or more further additional embodiments of
the disclosure, a particular device determines a selected link from
itself toward a root device in a computer network, wherein traffic
destined away from the root device via the particular device
utilizes the selected link in reverse from an intermediate device.
Upon receiving a discovery message at the particular device in
response to the intermediate device detecting that a data message
transmitted over the selected link in reverse did not reach the
particular device, wherein the discovery message is received from a
neighbor device other than the intermediate device, the particular
device triggers a local link repair of the selected link from the
particular device toward the root device to determine a new
selected link from the particular device toward the root device,
wherein traffic destined away from the root device via the
particular device utilizes the new selected link in reverse from
another intermediate device.
DESCRIPTION
[0024] A computer network is a geographically distributed
collection of nodes interconnected by communication links and
segments for transporting data between end nodes, such as personal
computers and workstations, or other devices, such as sensors, etc.
Many types of networks are available, ranging from local area
networks (LANs) to wide area networks (WANs). LANs typically
connect the nodes over dedicated private communications links
located in the same general physical location, such as a building
or campus. WANs, on the other hand, typically connect
geographically dispersed nodes over long-distance communications
links, such as common carrier telephone lines, optical lightpaths,
synchronous optical networks (SONET), synchronous digital hierarchy
(SDH) links, or Powerline Communications (PLC) such as IEEE 61334,
IEEE P1901.2, and others. In addition, a Mobile Ad-Hoc Network
(MANET) is a kind of wireless ad-hoc network, which is generally
considered a self-configuring network of mobile routes (and
associated hosts) connected by wireless links, the union of which
forms an arbitrary topology.
[0025] Smart object networks, such as sensor networks, in
particular, are a specific type of network having spatially
distributed autonomous devices such as sensors, actuators, etc.,
that cooperatively monitor physical or environmental conditions at
different locations, such as, e.g., energy/power consumption,
resource consumption (e.g., water/gas/etc. for advanced metering
infrastructure or "AMI" applications) temperature, pressure,
vibration, sound, radiation, motion, pollutants, etc. Other types
of smart objects include actuators, e.g., responsible for turning
on/off an engine or perform any other actions. Sensor networks, a
type of smart object network, are typically shared-media networks,
such as wireless or PLC networks. That is, in addition to one or
more sensors, each sensor device (node) in a sensor network may
generally be equipped with a radio transceiver or other
communication port such as PLC, a microcontroller, and an energy
source, such as a battery. Often, smart object networks are
considered field area networks (FANs), neighborhood area networks
(NANs), etc. Generally, size and cost constraints on smart object
nodes (e.g., sensors) result in corresponding constraints on
resources such as energy, memory, computational speed and
bandwidth. Correspondingly, a reactive routing protocol may, though
need not, be used in place of a proactive routing protocol for
smart object networks.
[0026] FIG. 1 is a schematic block diagram of an example computer
network 100 illustratively comprising nodes/devices 125 (e.g.,
labeled as shown, "root," "11," "12," . . . "45," and described in
FIG. 2 below) interconnected by various methods of communication.
For instance, the links 105 may be wired links and/or shared media
(e.g., wireless links, PLC links, etc.), where certain nodes 125,
such as, e.g., routers, sensors, computers, etc., may be in
communication with other nodes 125, e.g., based on distance, signal
strength, current operational status, location, etc. In addition,
various other devices, such as a head-end application device,
Central Intelligence Controller (CIC), or a network management
server (NMS) 150 (generally referred to herein as "NMS 150") may be
present in the network 100, such as via a WAN reachable by node
11-45 through the root node. Those skilled in the art will
understand that any number of nodes, devices, links, etc. may be
used in the computer network, and that the view shown herein is for
simplicity.
[0027] Data packets 140 (e.g., traffic and/or messages) may be
exchanged among the nodes/devices of the computer network 100 using
predefined network communication protocols such as certain known
wired protocols, wireless protocols (e.g., IEEE Std. 802.15.4,
WiFi, Bluetooth.RTM., etc.), PLC protocols, or other shared-media
protocols where appropriate. In this context, a protocol consists
of a set of rules defining how the nodes interact with each
other.
[0028] FIG. 2 is a schematic block diagram of an example
node/device 200 that may be used with one or more embodiments
described herein, e.g., as any of the devices 125 shown in FIG. 1
above, and also NMS 150. The device may comprise one or more
network interfaces 210 (e.g., wired, wireless, PLC, etc.), at least
one processor 220, and a memory 240 interconnected by a system bus
250, as well as a power supply 260 (e.g., battery, plug-in,
etc.).
[0029] The network interface(s) 210 contain the mechanical,
electrical, and signaling circuitry for communicating data over
links 105 coupled to the network 100. The network interfaces may be
configured to transmit and/or receive data using a variety of
different communication protocols. Note, further, that the nodes
may have two different types of network connections 210, e.g.,
wireless and wired/physical connections, and that the view herein
is merely for illustration. Also, while the network interface 210
is shown separately from power supply 260, for PLC the network
interface 210 may communicate through the power supply 260, or may
be an integral component of the power supply. In some specific
configurations the PLC signal may be coupled to the power line
feeding into the power supply.
[0030] It should be noted that PLC lines share many characteristics
with low power radio (wireless) technologies. In particular, though
each device in a given PLC network may each be connected to the
same physical power-line, a PLC link is very much a multi-hop link,
and connectivity is highly unpredictable, thus requiring multi-hop
routing when the signal is too weak. For instance, even in a
building the average number of hops is between two and three (even
larger when having to cross phases), while on an AMI network, on
the same power phase line, the number of hops may vary during a day
between one and 15-20. Those skilled in the art would recognize
that due to various reasons, including long power lines,
interferences, etc., a PLC connection may traverse multiple hops.
In other words, PLC cannot be seen as a "flat wire" equivalent to
broadcast media (such as Ethernet), since they are multi-hop
networks by essence.
[0031] The memory 240 comprises a plurality of storage locations
that are addressable by the processor 220 and the network
interfaces 210 for storing software programs and data structures
associated with the embodiments described herein. Note that certain
devices may have limited memory or no memory (e.g., no memory for
storage other than for programs/processes operating on the device
and associated caches). The processor 220 may comprise necessary
elements or logic adapted to execute the software programs and
manipulate the data structures 245. An operating system 242,
portions of which are typically resident in memory 240 and executed
by the processor, functionally organizes the device by, inter alia,
invoking operations in support of software processes and/or
services executing on the device. These software processes and/or
services may comprise routing process/services 244, a directed
acyclic graph (DAG) process 246, and an illustrative link
management process 248, as described herein. Note that while link
management process 248 is shown in centralized memory 240,
alternative embodiments provide for the process to be specifically
operated within the network interfaces 210, such as a component of
a MAC layer (process "248a").
[0032] It will be apparent to those skilled in the art that other
processor and memory types, including various computer-readable
media, may be used to store and execute program instructions
pertaining to the techniques described herein. Also, while the
description illustrates various processes, it is expressly
contemplated that various processes may be embodied as modules
configured to operate in accordance with the techniques herein
(e.g., according to the functionality of a similar process).
Further, while the processes have been shown separately, those
skilled in the art will appreciate that processes may be routines
or modules within other processes.
[0033] Routing process (services) 244 contains computer executable
instructions executed by the processor 220 to perform functions
provided by one or more routing protocols, such as proactive or
reactive routing protocols as will be understood by those skilled
in the art. These functions may, on capable devices, be configured
to manage a routing/forwarding table (a data structure 245)
containing, e.g., data used to make routing/forwarding decisions.
In particular, in proactive routing, connectivity is discovered and
known prior to computing routes to any destination in the network,
e.g., link state routing such as Open Shortest Path First (OSPF),
or Intermediate-System-to-Intermediate-System (ISIS), or Optimized
Link State Routing (OLSR). Reactive routing, on the other hand,
discovers neighbors (i.e., does not have an a priori knowledge of
network topology), and in response to a needed route to a
destination, sends a route request into the network to determine
which neighboring node may be used to reach the desired
destination. Example reactive routing protocols may comprise Ad-hoc
On-demand Distance Vector (AODV), Dynamic Source Routing (DSR),
DYnamic MANET On-demand Routing (DYMO), etc. Notably, on devices
not capable or configured to store routing entries, routing process
244 may consist solely of providing mechanisms necessary for source
routing techniques. That is, for source routing, other devices in
the network can tell the less capable devices exactly where to send
the packets, and the less capable devices simply forward the
packets as directed.
[0034] Notably, mesh networks have become increasingly popular and
practical in recent years. In particular, shared-media mesh
networks, such as wireless or PLC networks, etc., are often on what
is referred to as Low-Power and Lossy Networks (LLNs), which are a
class of network in which both the routers and their interconnect
are constrained: LLN routers typically operate with constraints,
e.g., processing power, memory, and/or energy (battery), and their
interconnects are characterized by, illustratively, high loss
rates, low data rates, and/or instability. LLNs are comprised of
anything from a few dozen and up to thousands or even millions of
LLN routers, and support point-to-point traffic (between devices
inside the LLN), point-to-multipoint traffic (from a central
control point such at the root node to a subset of devices inside
the LLN) and multipoint-to-point traffic (from devices inside the
LLN towards a central control point).
[0035] An example implementation of LLNs is an "Internet of Things"
network. Loosely, the term "Internet of Things" or "IoT" may be
used by those in the art to refer to uniquely identifiable objects
(things) and their virtual representations in a network-based
architecture. In particular, the next frontier in the evolution of
the Internet is the ability to connect more than just computers and
communications devices, but rather the ability to connect "objects"
in general, such as lights, appliances, vehicles, HVAC (heating,
ventilating, and air-conditioning), windows and window shades and
blinds, doors, locks, etc. The "Internet of Things" thus generally
refers to the interconnection of objects (e.g., smart objects),
such as sensors and actuators, over a computer network (e.g., IP),
which may be the Public Internet or a private network. Such devices
have been used in the industry for decades, usually in the form of
non-IP or proprietary protocols that are connected to IP networks
by way of protocol translation gateways. With the emergence of a
myriad of applications, such as the smart grid, smart cities, and
building and industrial automation, and cars (e.g., that can
interconnect millions of objects for sensing things like power
quality, tire pressure, and temperature and that can actuate
engines and lights), it has been of the utmost importance to extend
the IP protocol suite for these networks.
[0036] An example protocol specified in an Internet Engineering
Task Force (IETF) Internet Draft, entitled "RPL: IPv6 Routing
Protocol for Low Power and Lossy
Networks"<draft-ietf-roll-rpl-19> by Winter, at al. (Mar. 13,
2011 version), provides a mechanism that supports
multipoint-to-point (MP2P) traffic from devices inside the LLN
towards a central control point (e.g., LLN Border Routers (LBRs) or
"root nodes/devices" generally), as well as point-to-multipoint
(P2MP) traffic from the central control point to the devices inside
the LLN (and also point-to-point, or "P2P" traffic). RPL
(pronounced "ripple") may generally be described as a distance
vector routing protocol that builds a Directed Acyclic Graph (DAG)
for use in routing traffic/packets 140, in addition to defining a
set of features to bound the control traffic, support repair, etc.
Notably, as may be appreciated by those skilled in the art, RPL
also supports the concept of Multi-Topology-Routing (MTR), whereby
multiple DAGs can be built to carry traffic according to individual
requirements.
[0037] A DAG is a directed graph having the property that all edges
(and/or vertices) are oriented in such a way that no cycles (loops)
are supposed to exist. All edges are contained in paths oriented
toward and terminating at one or more root nodes (e.g.,
"clusterheads or "sinks"), often to interconnect the devices of the
DAG with a larger infrastructure, such as the Internet, a wide area
network, or other domain. In addition, a Destination Oriented DAG
(DODAG) is a DAG rooted at a single destination, i.e., at a single
DAG root with no outgoing edges. A "parent" of a particular node
within a DAG is an immediate successor of the particular node on a
path towards the DAG root, such that the parent has a lower "rank"
than the particular node itself, where the rank of a node
identifies the node's position with respect to a DAG root (e.g.,
the farther away a node is from a root, the higher is the rank of
that node). Further, in certain embodiments, a sibling of a node
within a DAG may be defined as any neighboring node which is
located at the same rank within a DAG. Note that siblings do not
necessarily share a common parent, and routes between siblings are
generally not part of a DAG since there is no forward progress
(their rank is the same). Note also that a tree is a kind of DAG,
where each device/node in the DAG generally has one parent or one
preferred parent.
[0038] DAGs may generally be built (e.g., by DAG process 246) based
on an Objective Function (OF). The role of the Objective Function
is generally to specify rules on how to build the DAG (e.g. number
of parents, backup parents, etc.).
[0039] In addition, one or more metrics/constraints may be
advertised by the routing protocol to optimize the DAG against.
Also, the routing protocol allows for including an optional set of
constraints to compute a constrained path, such as if a link or a
node does not satisfy a required constraint, it is "pruned" from
the candidate list when computing the best path. (Alternatively,
the constraints and metrics may be separated from the OF.)
Additionally, the routing protocol may include a "goal" that
defines a host or set of hosts, such as a host serving as a data
collection point, or a gateway providing connectivity to an
external infrastructure, where a DAG's primary objective is to have
the devices within the DAG be able to reach the goal. In the case
where a node is unable to comply with an objective function or does
not understand or support the advertised metric, it may be
configured to join a DAG as a leaf node. As used herein, the
various metrics, constraints, policies, etc., are considered "DAG
parameters."
[0040] Illustratively, example metrics used to select paths (e.g.,
preferred parents) may comprise cost, delay, latency, bandwidth,
expected transmission count (ETX), etc., while example constraints
that may be placed on the route selection may comprise various
reliability thresholds, restrictions on battery operation,
multipath diversity, bandwidth requirements, transmission types
(e.g., wired, wireless, etc.). The OF may provide rules defining
the load balancing requirements, such as a number of selected
parents (e.g., single parent trees or multi-parent DAGs). Notably,
an example for how routing metrics and constraints may be obtained
may be found in an IETF Internet Draft, entitled "Routing Metrics
used for Path Calculation in Low Power and Lossy
Networks"<draft-ietf-roll-routing-metrics-19> by Vasseur, et
al. (Mar. 1, 2011 version). Further, an example OF (e.g., a default
OF) may be found in an IETF Internet Draft, entitled "RPL Objective
Function 0"<draft-ietf-roll-of0-15> by Thubert (Jul. 8, 2011
version) and "The Minimum Rank Objective Function with
Hysteresis"<draft-ietf-roll-minrank-hysteresis-of-04> by O.
Gnawali et al. (May 17, 2011 version).
[0041] Building a DAG may utilize a discovery mechanism to build a
logical representation of the network, and route dissemination to
establish state within the network so that routers know how to
forward packets toward their ultimate destination. Note that a
"router" refers to a device that can forward as well as generate
traffic, while a "host" refers to a device that can generate but
does not forward traffic. Also, a "leaf" may be used to generally
describe a non-router that is connected to a DAG by one or more
routers, but cannot itself forward traffic received on the DAG to
another router on the DAG. Control messages may be transmitted
among the devices within the network for discovery and route
dissemination when building a DAG.
[0042] According to the illustrative RPL protocol, a DODAG
Information Object (DIO) is a type of DAG discovery message that
carries information that allows a node to discover a RPL Instance,
learn its configuration parameters, select a DODAG parent set, and
maintain the upward routing topology. In addition, a Destination
Advertisement Object (DAO) is a type of DAG discovery reply message
that conveys destination information upwards along the DODAG so
that a DODAG root (and other intermediate nodes) can provision
downward routes. A DAO message includes prefix information to
identify destinations, a capability to record routes in support of
source routing, and information to determine the freshness of a
particular advertisement. Notably, "upward" or "up" paths are
routes that lead in the direction from leaf nodes towards DAG
roots, e.g., following the orientation of the edges within the DAG.
Conversely, "downward" or "down" paths are routes that lead in the
direction from DAG roots towards leaf nodes, e.g., generally going
in the opposite direction to the upward messages within the
DAG.
[0043] Generally, a DAG discovery request (e.g., DIO) message is
transmitted from the root device(s) of the DAG downward toward the
leaves, informing each successive receiving device how to reach the
root device (that is, from where the request is received is
generally the direction of the root). Accordingly, a DAG is created
in the upward direction toward the root device. The DAG discovery
reply (e.g., DAO) may then be returned from the leaves to the root
device(s) (unless unnecessary, such as for UP flows only),
informing each successive receiving device in the other direction
how to reach the leaves for downward routes. Nodes that are capable
of maintaining routing state may aggregate routes from DAO messages
that they receive before transmitting a DAO message. Nodes that are
not capable of maintaining routing state, however, may attach a
next-hop parent address. The DAO message is then sent directly to
the DODAG root that can in turn build the topology and locally
compute downward routes to all nodes in the DODAG. Such nodes are
then reachable using source routing techniques over regions of the
DAG that are incapable of storing downward routing state. In
addition, RPL also specifies a message called the DIS (DODAG
Information Solicitation) message that is sent under specific
circumstances so as to discover DAG neighbors and join a DAG or
restore connectivity.
[0044] FIG. 3 illustrates an example simplified control message
format 300 that may be used for discovery and route dissemination
when building a DAG, e.g., as a DIO, DAO, or DIS message. Message
300 illustratively comprises a header 310 with one or more fields
312 that identify the type of message (e.g., a RPL control
message), and a specific code indicating the specific type of
message, e.g., a DIO, DAO, or DIS. Within the body/payload 320 of
the message may be a plurality of fields used to relay the
pertinent information. In particular, the fields may comprise
various flags/bits 321, a sequence number 322, a rank value 323, an
instance ID 324, a DODAG ID 325, and other fields, each as may be
appreciated in more detail by those skilled in the art. Further,
for DAO messages, additional fields for destination prefixes 326
and a transit information field 327 may also be included, among
others (e.g., DAO_Sequence used for ACKs, etc.). For any type of
message 300, one or more additional sub-option fields 328 may be
used to supply additional or custom information within the message
300. For instance, an objective code point (OCP) sub-option field
may be used within a DIO to carry codes specifying a particular
objective function (OF) to be used for building the associated DAG.
Alternatively, sub-option fields 328 may be used to carry other
certain information within a message 300, such as indications,
requests, capabilities, lists, notifications, etc., as may be
described herein, e.g., in one or more type-length-value (TLV)
fields.
[0045] FIG. 4 illustrates an example simplified DAG that may be
created, e.g., through the techniques described above, within
network 100 of FIG. 1. For instance, certain links 105 may be
selected for each node to communicate with a particular parent (and
thus, in the reverse, to communicate with a child, if one exists).
These selected links form the DAG 410 (shown as bolded lines),
which extends from the root node toward one or more leaf nodes
(nodes without children). Traffic/packets 140 (shown in FIG. 1) may
then traverse the DAG 410 in either the upward direction toward the
root or downward toward the leaf nodes, particularly as described
herein.
[0046] As noted above, one significant challenge with routing in
LLNs is ensuring that links to neighboring nodes are valid. More
traditional IP networks typically use a proactive keepalive
mechanism with a relatively short period, such as the Bidirectional
Forwarding Detection (BFD) protocol. Due to the strict resource
constraints of LLNs, protocols such as RPL do not rely on proactive
keepalive mechanisms. Instead, many LLN protocols typically take a
reactive approach, using link-layer acknowledgments and/or IPv6
Neighbor Unreachability Detection (NUD) to update link statistics
when forwarding traffic.
[0047] Consider, for example, the illustrative cases of a packet
140 sent in the UPWARD direction (i.e., from a network device in
the DAG 410 toward/to the root) and in the reverse DOWNWARD
direction, (i.e., away from the root toward a particular network
device). First, in the UPWARD direction, assume that link 33-22 is
down. When node 33 attempts to forward a packet in the UPWARD
direction across link 33-22, the node 33 will detect that the link
is down, and attempts to select an alternate next-hop (e.g., node
23) or else trigger a local routing repair to find another set of
next-hops to send the packet. This reactive approach works well in
the UPWARD direction. However, as described below, such a reactive
approach does not work as well in the DOWNWARD direction.
[0048] In particular, for the DOWNWARD direction, consider a packet
140 sent from the root to node 33. When using source routing, the
root will determine a source route from the root to node 33 (e.g.,
root-12-22-33), append the source route (e.g., using an IPv6
Routing Header), and forwards the packet to node 12. However, when
the packet reaches the failing link (e.g., link 22-33), the packet
will be dropped.
[0049] The fundamental problem is that nodes only maintain links in
the UPWARD direction and detect link failures reactively when
sending a data packet (generally to avoid proactive keepalive
messages). If node 33 has no data packets to send, it will not
detect the link failure and will not notify the root that link
22-33 is no longer valid. As a result, the root will continue to
send traffic down an invalid path.
[0050] Unlike forwarding packets in the UPWARD direction, it is
much more difficult to build and repair a routing topology when
detecting link failures in the downward direction. In particular,
many LLN protocols (e.g., RPL) build routing topologies in the
UPWARD direction and reverse the links for use in the DOWNWARD
direction. With such protocols, it is the responsibility of devices
to maintain their links towards the root. In particular, if node 22
detects that link 22-33 is down, it cannot simply send a message to
node 33 to find a new path.
[0051] Note that in certain systems, such as unconstrained IP
networks, nodes can send regular proactive keepalive messages, then
the routing topology will be kept up-to-date on the timescales of
the keepalive period. While a short keepalive period will detect
link failures more quickly, doing so is costly in
resource-constrained environments such as LLNs (e.g., limited
energy and channel capacity). In addition, the root could also
maintain multiple (diverse) paths and send multiple copies of the
packet along each path to increase the likelihood of at least one
being received by the destination. However, applying this technique
to all traffic is also costly in resource-constrained
environments.
[0052] Data-Triggered Link Repair
[0053] The techniques herein are directed to a distributed
mechanism of discovering a failed link or an improperly utilized
link (e.g., from node 22 to node 33) and triggering the downlink
node (node 33) to perform a link local repair to maintain
end-to-end connectivity. Specifically, according to one or more
embodiments of the disclosure as described in detail below, an
intermediate device transmits a data message away from a root
device toward a receiver device in a computer network, the data
message transmitted by utilizing, in reverse, a link that had been
previously selected by the receiver device toward the root device.
In response to detecting that the data message did not reach the
receiver device, a discovery message is may be sent to one or more
neighbor devices, wherein the discovery message carries an
identification (ID) of the receiver device and a discovery scope
indicating how many hops the discovery message is allowed to
traverse to reach the receiver device, and wherein the receiver
device, upon receiving the discovery message, triggers a local link
repair of the link from the receiver device toward the root
device.
[0054] Illustratively, the techniques described herein may be
performed by hardware, software, and/or firmware, such as in
accordance with the link management process 248/248a, which may
contain computer executable instructions executed by the processor
220 (or independent processor of interfaces 210) to perform
functions relating to the techniques described herein, e.g., in
conjunction with routing process 244 (and/or DAG process 246). For
example, the techniques herein may be treated as extensions to
conventional protocols, such as the RPL protocol or else various
communication protocols, and as such, may be processed by similar
components understood in the art that execute those protocols,
accordingly. Notably, the techniques herein are not limited to RPL,
and could be used with all routing protocols built according to the
same paradigm.
[0055] Operationally, the techniques herein may be generally based
on devices within the network determining a selected link from
itself toward a root device in a computer network 100, where
traffic destined away from the root device via the particular
device utilizes the selected link in reverse, e.g., from an
intermediate device. Illustratively, an example routing protocol
that operates in this manner is RPL, creating DAGs 410 as described
above, though other routing protocols that function similarly in
this manner (e.g., other distance vector protocols) may also be
utilized.
[0056] In accordance with one or more specific embodiments herein,
as the routing topology (e.g., DAG 410) is being built, each node
may build a cache/list (e.g., data structure 245) of one-hop
neighbors, e.g., based on the source address of the DIOs. For
example based on the connectivity shown in FIGS. 1 and 4, the
neighbor cache of the certain select nodes might be:
[0057] Root: 11, 12, 13;
[0058] 12: Root, 11, 22, 23;
[0059] 22: 11, 12, 23, 32, 33;
[0060] 32: 21, 22, 31, 33, 42, 43;
[0061] 33: 22, 23, 32, 34, 43, 44;
[0062] 42: 32, 33, 44;
[0063] 43: 33, 34, 43, 45;
[0064] Etc.
[0065] As shown in FIG. 5, an intermediate device, e.g., node 22,
may attempt to transmit a data message 540 (e.g., a packet 140)
away from a root device toward a receiver device (e.g., node 33),
which may be the destination of the message or merely another
transit/intermediate node. In particular, as noted above, the data
message may be transmitted by utilizing, in reverse, a link that
had been previously selected by the receiver device toward the root
device, e.g., the DAG link. However, based on not receiving a
layer-2 acknowledgement (ACK) 545, or based on receiving an
explicit error notification, such as an IPv6 NUD, the intermediate
device may correspondingly detecting that the data message did not
reach the receiver device.
[0066] At this time, the intermediate device (node 22) may drop the
original data message 540, and enters into an illustrative
"sub-node discovery mode" to take various actions described herein
in order to try to somehow "nudge" the sub-node (the receiver
device) to "wakeup" and trigger a topology repair. In one
embodiment, as shown in FIG. 6A, in response to detecting that the
data message 540 did not reach the receiver device, the
intermediate device may send a discovery message 640 to one or more
neighbor devices (e.g., node 23 and node 32), such as a unicast
message to each neighbor, or a multicast (or possibly even
broadcast) to the corresponding neighbor nodes. The general goal of
the discovery message 640 is to reach the receiver device (e.g.,
node 33), such that the receiver device may trigger a local link
repair of the link from the receiver device toward the root device,
to correct the topology, accordingly.
[0067] Notably, in another embodiment herein in addition to
originating the discovery message 640 by the intermediate device
detecting the failed link, that intermediate device may
alternatively (or in addition) notify the source of the data
message 540 (e.g., the root node or any other nodes in the network
when using source routing reactive routing such as with RPL P2P)
that the data message did not reach the receiver device. As shown
in FIG. 6B, the intermediate device (e.g., node 22) may return a
notification 650, such as an Internet Control Message Protocol
(ICMP) error message, to the source in order to prompt the source
to resend the data message 540' using the same broken path (after
caching) after having set a newly defined bit illustratively called
the "S" bit (Search bit). In source routing, in particular, the S
bit may be hop specific (e.g., in the IPv6 hop-by-hop header), and
may be set in the slot right after the intermediate node that
originally sent the error message, i.e., corresponding to the
receiver device. As such, upon receiving the repeated data message
540', the penultimate hop may encapsulate the data message into a
multicast local search packet, that is, discovery message 640
(e.g., with a limited TTL as described below).
[0068] Note further that in addition to source route correction,
other reasons exist herein for sending the notification 650 to the
source. For example, such notifications may be used to keep track
of the number of times the route was outdated, to maintain logs
that could provide a basis for changing various network parameters
at the root level (e.g., increased refresh frequency) or to provide
input to a central agent (the NMS 150).
[0069] In general, as illustrated in FIG. 6C, a node does not send
the discovery message (particularly when unicast) to nodes with a
lesser rank, that is, sending the discovery message 540 to only
neighbor devices that are as far as or further than the device
itself from the root device. In this manner, only those nodes level
with or below the particular intermediate node detecting the
problem (or simply the neighbor device sending the discovery
message) are involved in the sub-node discovery.
[0070] Illustratively, with reference to FIG. 7, the discovery
message 640 (shown in simplified form) may comprise the sender's
rank value 642, a discovery scope value 644 (e.g., "2") indicating
how many hops the discovery message is allowed to traverse to reach
the receiver device, and the sub-node identifier (ID) 646, such as
an address. In addition, the discovery message 640 may, in certain
embodiments described herein, encapsulate the original (or
retransmission of the original) data message 540, to be
decapsulated by the receiver device when/if reached.
[0071] Upon receiving a discovery message 640, neighbor devices
(equal or lower nodes) may look into their neighbor cache list and
see if there is a match for the sub-node's ID in field 646. That
is, the devices receiving the discovery message 640 may be
configured to determine whether the receiver device is reachable by
the particular device. As shown in FIG. 8A, assuming the link 32-33
exists, then in response to the receiver device being reachable,
the neighbor device (node 32) may forward the discovery message
directly to the receiver device (e.g., node 33).
[0072] Said differently, a node processing the discovery message
640 (e.g., an encapsulated data message with the S bit set) may
find that the "searched" node is present in its routing table or
explicit neighbor list. In one embodiment, the device may relay the
discovery message 640 (or simply the decapsulated data message 540)
to the receiver device, or may alternatively, or in addition, send
a reply (notification 850) back to the requestor. For example,
assume in FIG. 8B that node 23 also receives the discovery message
640, and in which case (and where the receiver device is reachable
over a proper path), node 23 sends a reply message (notification
850) back to the node 22 to inform it of the correct/proper path to
the receiver device (e.g., the DAG 410, or else the link
23-23).
[0073] In response to the receiver device not being reachable,
however, as shown in FIG. 8C (assuming the link 32-33 is not
available, nor the link 22-23, for illustration purposes), the
neighbor device (e.g., node 32) may decrement the discovery scope
644, and, if the decremented discovery scope is non-zero, may
forward the discovery message 640 to one or more further neighbor
devices (e.g., except parents) of the particular device.
[0074] Illustratively, the discovery scope value 644 may be
pre-configured as the routing topology is built (e.g., a DAG with
RPL), such as a discovery scope (or time-to-live, "TTL") value of
2. The discovery scope parameter can be provided to each node in
the network by a dynamic host configuration protocol (DHCP) server,
the NMS 150, etc. In certain embodiments, the discovery scope may
be dynamically computed by a head-end application (e.g., on the NMS
150) by observing the success/failure rate of the techniques
herein. By having a discovery scope, propagation of the discovery
messages 640 is limited (so as not to flood the entire network),
creating a boundary of the search.
[0075] Referring still to FIG. 8C, node 32 receives and processes
the message, and since node 33 is not in its cache, node 32 will
regenerate and send the discovery message 640 to nodes 21, 31, 42,
and 43, with decremented discovery scope=1. (Note that the message
640 is not sent to node 22 again, as it was the sender.) Now, with
reference to FIG. 8D, node 43 will find node 33 in its cache, and
will send the discovery message 640 with (discovery scope=0) and
destination address as node 33.
[0076] Upon receiving this discovery message, as shown in FIG. 9,
node 33 triggers a link-topology (local link) repair of the
selected link toward the root device, thus selecting a new link for
the topology (e.g., link 33-23 for DAG 410). Notably, nodes
propagating the discovery message 640 will eventually stop the
relay of the discovery message when the discovery scope (TTL) value
reaches 0.
[0077] Note also that if the discovery message 640 carried an
encapsulated data message 540, this may be decapsulated by the
receiver device, and processed accordingly (e.g., forwarded or
locally processed). That is, in one or more specific embodiments,
the entire data message 540 may be embedded in the discovery
message 640, rather than dropping it. Although the size of the
discovery message is correspondingly increased (and thus the
bandwidth usage), the message would generally reach its
destination, thus avoiding having the original source resend its
lost/dropped message.
[0078] Additionally, it is possible that the sub-node (receiver
device) to be discovered may be beyond the configured search scope.
In this case, the link topology will not be repaired as the
targeted node will not receive the discovery message 640. In this
case, upon determining that the discovery message did not reach the
receiver node, the intermediate node triggering the sub-node
discovery (node 23) can increment the discovery scope value 644,
such that is it increased for a subsequently sent discovery message
to that same receiver (e.g., trying again, or else in response to a
next received data message destined via the failed receiver device
link).
[0079] In yet another embodiment described herein, to limit the
sub-mode discovery mechanism, nodes transmitting discovery messages
may "serialize" their search, i.e., sending the discovery message
one discovery scope "level" at a time. For instance, each neighbor
device receiving the discovery message checks whether it can reach
the receiver device, and if so, notifies the intermediate device,
as mentioned above. If it cannot reach the receiver device, then
the neighbor device delays a configured time before forwarding the
discovery message to a next discovery scope level, unless receiving
an instruction sent to neighbor device to cease forwarding the
discovery message in response to the previous message sender
receiving a notification that a particular neighbor device can
reach the receiver device. FIG. 10A illustrates an example, where
if a node sends k discovery messages n1, n2, n3, . . . , nk, upon
receiving the message each node does a search in its cache and arms
a timer T. If one of the k nodes finds the searched node (e.g.,
node 33), as shown in FIG. 10B, that node sends a newly defined
message 1050 to the requester (for example node 32 would send such
a message) indicating that the searched node was found. Upon
receiving that newly defined message 1050, the requester sends a
link local message 1055 cancelling its original search request,
thus stopping the process. On the other hand, if in FIG. 10B there
were no nodes that could reach the receiver device, as in the
topology of FIG. 10C, then those nodes may also further send the
discovery message upon expiration of the timer T. Using such a
timer-based search allows for reducing the number of searches in
very dense environments, even if its slows down the repair (which
may not be an issue). Note that the value of T may be dynamically
computed according to the number of nodes to which the discovery
messages may be sent.
[0080] Note that the downward-link problem also directly relates to
erroneous source-route computation (e.g., logic errors, routing
table corruption, missing DAOs, etc.). That is, when source-routing
is used, there might be a number of reasons why such a source
routed path may become inactive. For instance, in addition to the
link failing without the receiver node being aware of the failure,
other causes for source-routing failures may include, among others,
where the link (e.g., the 22-33 link) may become weak or fail, and
the receiving node 33 may have selected node 23 as its new best
next hop, but where the source-routing device (e.g., the root node)
is unaware of the change.
[0081] For example, routing protocols generally have mechanisms to
inform other nodes of routing topology changes. For the sake of
illustration, Link State would flood a new LSA (Link State
Advertisement) whereby a distance vector routing protocol such as
RPL would send a control plane message (e.g., a DAO) that would
inform the nodes of the routing topology change. Upon receiving
such a message, the receiving node (e.g., the root node) would
update its network database to reflect the change and compute a new
source-routed path upon receiving a packet destined to that node
(or pre-compute such a path). Unfortunately, such notifications may
be lost, not properly processed by the receiving nodes, the routing
entry may not be updated (a corrupted routing table), etc., thus
resulting in the root node (or other source-routing node)
constantly sending data messages 540 to a node along a broken
source-routed path without any way to repair the DOWNWARD path.
(Note that even with DAO acknowledgement, there are a number of
reasons why such notifications may still be improperly processed or
lost in the network.)
[0082] As shown in FIG. 11A, for instance, when a data message 540
is sent from the root node to node 33 along the root-12-22-33
source-routed broken path, when the last node/router along the path
sends the packet (node 22), two situations may occur. First, the
link (22-33) is still operational, but not used anymore by the
next-hop node (node 33) which has selected a new best path (i.e.,
an improper use of the unselected link). Second, the link may have
failed, in which case the link failure will be detected (lack of
ACK, NUD) by the sending node, and the techniques above may be
again utilized.
[0083] According to one or more embodiments herein, therefore,
additional components are described herein with regard to the first
case, where node 33 would receive a packet (data message 540) from
a non-preferred next hop (i.e., over an improper, unselected link),
as shown in FIG. 11A. Should this occur, then as shown in FIG. 11B,
the receiver device (node 33) may sends a notification 1150 back to
the intermediate device, or more particularly to the source routing
originator/sender (or the entire network in the case of a link
state protocol), such as a new DAO message in the case of RPL,
notifying the device(s) of improper use of the unselected link and
thus triggering a database update and new source-route path
computation by the source device (e.g., the root node). The source
device (e.g., root node) may then try to process this notification
1150, and attempts to correct the source-route path.
[0084] Note, however, that it is possible that the source-routed
path may still point to the improper link (i.e., the same erroneous
path) due to a processing error (logic error) or a corrupted
routing table. Upon detecting this condition, that is, determining
that more than a configured number of improper uses of unselected
links have occurred at the particular receiver device, then a
management device (e.g., NMS 150) may be notified of the improper
uses. In this case, the management device may then take more
appropriate corrective action regarding the improper uses, such as
performing a software upgrade to correct spurious code.
[0085] FIG. 12 illustrates an example simplified procedure for
efficient link repair mechanism triggered by data traffic in a
computer network in accordance with one or more embodiments
described herein, particularly from the perspective of the device
utilizing the broken/improper link (e.g., node 22 above). The
procedure 1200 may start at step 1205, and continues to step 1210,
where, as described in greater detail above, an intermediate device
(e.g., node 22) transmits a data message 540 away from a root
device toward a receiver device (e.g., node 33) in a computer
network 100, the data message transmitted by utilizing, in reverse,
a link that had been previously selected by the receiver device
toward the root device.
[0086] Upon detecting in step 1215 that the data message did not
reach the receiver device, such as through a NUD or no ACK, the
intermediate device may send a discovery message 640 in step 1220
to one or more neighbor devices, wherein the discovery message
carries an ID 646 of the receiver device and a discovery scope 644
indicating how many hops the discovery message is allowed to
traverse to reach the receiver device. Note that as mentioned
above, the source device (e.g., the root) may resend the data
message 540, or else the intermediate device detecting the broken
link may self-initiate the discovery messages, accordingly. As
described herein (e.g., and with reference to FIG. 14), the
receiver device, upon receiving the discovery message, thus
triggers a local link repair of the link from the receiver device
toward the root device. Optionally (e.g., in certain specific
embodiments and situations), in step 1225, the intermediate device
may receive a reply to the discovery message from a particular
neighbor device that can reach the receiver device, wherein the
reply carries a proper path to the receiver device. The procedure
1200 illustratively ends in step 1230.
[0087] In addition, FIG. 13 illustrates an example simplified
procedure for efficient link repair mechanism triggered by data
traffic in a computer network in accordance with one or more
embodiments described herein, particularly from the perspective of
a neighbor device attempting to reach the receiver device (e.g.,
device 32). The procedure 1300 may start at step 1305, and
continues to step 1310, where, as described in greater detail
above, the neighbor device (a particular device) may receive a
discovery message 640 in response to an intermediate device (e.g.,
nod 22) detecting that a data message 540 transmitted away from a
root device toward a receiver device (e.g., node 32) in a computer
network 100 did not reach the receiver device, wherein the data
message was transmitted utilizing, in reverse, a link that had been
previously selected by the receiver device toward the root device.
Again, the discovery message 640 carries an ID 646 of the receiver
device and a discovery scope 644 indicating how many hops the
discovery message is allowed to traverse to reach the receiver
device.
[0088] In step 1315, the particular/neighbor device may determine
whether the receiver device is reachable by the particular device,
and if determined that it is in step 1320, then in step 1325 the
particular device may forward the discovery message 640 to the
receiver device, where the receiver device, upon receiving the
discovery message, triggers a local link repair of the link from
the receiver device toward the root device. Note also that in step
1325, the particular device in certain embodiments and situations
may reply to discovery message with a proper path 850, as noted
above.
[0089] If, on the other hand, it is determined at step 1320 that
the receiver device is not reachable, then in step 1330, the
particular/neighbor device may decrement the discovery scope value
644, and if non-zero in step 1335, then in step 1340 may forward
the discovery message to one or more further neighbor devices of
the particular device to continue searching for the receiver device
(e.g., in serialized manner as described above in one specific
embodiment). The procedure 1300 may then end in step 1345, having
transmitted the discovery message 640, or else in response to
dropping the message when the discovery scope reaches zero.
[0090] Moreover, FIG. 14 illustrates an example simplified
procedure for efficient link repair mechanism triggered by data
traffic in a computer network in accordance with one or more
embodiments described herein, particularly from the perspective of
the receiver device (e.g., node 33). The procedure 1400 may start
at step 1405, and continues to step 1410, where, as described in
greater detail above, the device determines a selected link from
itself toward a root device in a computer network 100, wherein
traffic destined away from the root device via the particular
device utilizes the selected link in reverse from an intermediate
device (e.g., node 22). In step 1415, the receiver device may
receive a discovery message 640 in response to the intermediate
device detecting that a data message transmitted over the selected
link in reverse did not reach the particular receiver device. That
is, the discovery message is received from a neighbor device other
than the intermediate device. Note that as mentioned above, the
receiver device may also optionally decapsulate a data message 540
from within the discovery message 640, if included therein in
specific embodiments.
[0091] In response to the discovery message, it can be assumed that
the link from the intermediate device (e.g., node 22) to the
receiver device (e.g., node 33) is broken, and thus in step 1420
the receiver device may trigger a local link repair of the selected
link from the particular device toward the root device to determine
a new selected link (where traffic destined away from the root
device via the particular device utilizes the new selected link in
reverse from another intermediate device, e.g., node 23). The
illustrative procedure 1400 may then end in step 1425.
[0092] Lastly, FIG. 15 illustrates another example simplified
procedure for efficient link repair mechanism triggered by data
traffic in a computer network in accordance with one or more
embodiments described herein, particularly from the perspective of
the receiver device when a link is used improperly. The procedure
1500 may start at step 1505, and continues to step 1510, where, as
described in greater detail above, the receiver device (e.g., node
33) may receive a data message 540 over an improper, unselected
link from a given intermediate device, e.g., node 22 in FIG. 11A
above, which is not on the DAG 410. According to the techniques
herein, in step 1515, the receiver device may then notify the given
intermediate device of the improper use of the unselected link. In
addition, if it is determined in step 1520 that there have been too
many improper uses of that link (or any link) to the receiver
device, then in step 1525, a management device (e.g., NMS 150) may
be notified of the improper uses, such that the management device
may take corrective action regarding the improper uses, as
described above. The procedure 1500 illustratively ends in step
1530.
[0093] It should be noted that while certain steps within
procedures 1200-1500 may be optional as described above, the steps
shown in FIGS. 12-15 are merely examples for illustration, and
certain other steps may be included or excluded as desired.
Further, while a particular order of the steps is shown, this
ordering is merely illustrative, and any suitable arrangement of
the steps may be utilized without departing from the scope of the
embodiments herein. Moreover, while procedures 1200-1500 are
described separately, certain steps from each procedure may be
incorporated into each other procedure, and the procedures are not
meant to be mutually exclusive.
[0094] The techniques described herein, therefore, provide for an
efficient link repair mechanism triggered by data traffic in a
computer network. In particular, the techniques herein provide a
distributed mechanism where in response to data traffic not
reaching a node (or not reaching it on its preferred path), that
node, once informed of the problem, may trigger corresponding local
link repair. Accordingly, the techniques herein address a
significant issue in networks that use reverse path routing,
significantly improving the path reliability and SLA, particularly
in constrained networks. Also, by triggering link repair based on
data traffic, that is, when a packet is being delivered along a
broken or discontinued path, network devices minimize overhead that
would be otherwise caused by keepalive messages.
[0095] While there have been shown and described illustrative
embodiments that provide for efficient link repair mechanism
triggered by data traffic in a computer network, it is to be
understood that various other adaptations and modifications may be
made within the spirit and scope of the embodiments herein. For
example, the embodiments have been shown and described herein with
relation to LLNs. However, the embodiments in their broader sense
are not as limited, and though well-suited for constrained
networks, may, in fact, be used with other types of networks and/or
protocols. In addition, while certain protocols are shown, such as
RPL, other suitable protocols may be used, accordingly. Also, while
the techniques generally describe the root node as the source
device, other devices, particularly head-end nodes and/or network
management system/server (NMS) devices, may also source data
messages (e.g., in the DOWNWARD direction).
[0096] The foregoing description has been directed to specific
embodiments. It will be apparent, however, that other variations
and modifications may be made to the described embodiments, with
the attainment of some or all of their advantages. For instance, it
is expressly contemplated that the components and/or elements
described herein can be implemented as software being stored on a
tangible (non-transitory) computer-readable medium (e.g.,
disks/CDs/etc.) having program instructions executing on a
computer, hardware, firmware, or a combination thereof. Accordingly
this description is to be taken only by way of example and not to
otherwise limit the scope of the embodiments herein. Therefore, it
is the object of the appended claims to cover all such variations
and modifications as come within the true spirit and scope of the
embodiments herein.
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